This invention relates to a hydraulic damper and, particularly to a hydraulic damper of the kind including a cylinder containing hydraulic liquid therein, a piston working in the cylinder and partitioning the interior thereof into first and second liquid chambers, a piston rod secured to the piston and extending to the outside, and a disc valve mounted on each side of the piston for generating the damping force. Usually, the disc valve exposed to the first liquid chamber opens when the piston moves toward the second liquid chamber and generates a damping force in that condition, and when the piston moves toward the first liquid chamber, the disc valve provided in the second liquid chamber acts to generate a damping force.
When a hydraulic damper of this kind is used in a suspension system of a vehicle such as an automobile wherein the damper is installed between the sprung mass and the unsprung mass of the vehicle, it is sometimes required that the damping force in the contraction stroke of the damper drastically be decreased compared with the damping force in the extension stroke of the damper, so as to improve the driving comfort of the vehicle.
The damping force of the disc valve is usually determined by the rigidity of the valve disc, thus, it is usually possible to determine the damping force as desired by changing the thickness and the material of the valve disc. However, when the desired damping force is not so large, the dimensional tolerance in the thickness of the valve disc has a large affect on the damping force.